Magnetic recording hard disk drives use a read/write transducer or head mounted on an air-bearing slider for reading and/or writing data to the disk. The slider is attached to an actuator arm by a suspension and positioned very close to the disk surface by the suspension. The combination of the slider and suspension is called the head-suspension assembly (HSA). There are typically a stack of disks in the disk drive with a HSA associated with each disk surface in the stack.
The separation between the slider and the disk surface is called the flying height. The slider rides on a cushion or bearing of air generated by the rotation of the disk. The slider is attached to a flexure on the suspension and the suspension includes a load beam that applies a load force to the slider to counteract the air-bearing force while permitting the slider to “pitch” and “roll”. The flying height and flying dynamics of the slider are influenced by factors such as the rotation speed of the disk, the aerodynamic shape of the air-bearing surface (ABS) of the slider, the load force applied to the slider by the suspension, and the pitch and roll torques applied to the slider by the suspension.
The desired pitch and roll torques are determined from the pitch static attitude (PSA) and roll static attitude (RSA) and the pitch and roll stiffnesses (Kp, Kr) of the suspension. These torques are called the pitch static torque (PST) and roll static torque (RST). Thus,                PST=KpPSA; and        RST=KrRSA.        
The slider pitch and roll dynamic or flying attitudes are determined by a force balance between the air-bearing force and the suspension load force and static torques (PST and RST). The deviations of the dynamic attitudes should be very small to achieve good performance and high reliability. The slider dynamic attitudes are very sensitive to PST and RST, especially in disk drives that use very small sliders or very-low-flying sliders, or disk drives with a relatively low rotational speed, such as the commercially available 1-inch disk drives. Therefore, it is important to reduce deviations in PST and RST and assure that all HSAs are manufactured with essentially the same PST and RST values.
In conventional HSA manufacturing, Kp and Kr are assumed to be constants that do not vary from one HSA to the next. Then, the deviations of PST and RST (dPST and dRST) can be expressed as:                dPST=KpdPSA; and        dRST=KrdRSA, where dPSA and dRSA are the deviations in PSA and RSA, respectively.Therefore, to reduce dPST and dRST, dPSA and dRSA are reduced by adjusting PSA and RSA. For example, some disk drive manufacturers mechanically adjust the PSA and RSA by bending a suspension component, such as the flexure. U.S. Pat. No. 6,011,239 describes a method for adjusting the PSA and RSA to the desired values by first measuring the PSA and RSA and then laser heating the flexure.        
Typically, the standard deviation of Kp and Kr is in the range of about 5% to 10%. However, it has recently been determined that the standard deviation of Kp and Kr can be as large as 23%. When there are relatively large non-zero PSA and RSA values (such as a PSA of 2.0 degrees), Kp and Kr deviations can also result in large dPST and dRST deviations even though dPSA and dRSA are zero. In reality the effect can be worse because adjustment of PSA and RSA can also change Kp and Kr.
Thus, what is needed is an HSA manufacturing process that adjusts PST and RST and assures that all HSAs have substantially the same values of PST and RST, regardless of deviations in Kp and Kr and PSA and RSA.